(a) Technical Field
The present disclosure relates generally to an apparatus and method for learning an engine friction torque of a hybrid vehicle. More particularly, the present disclosure relates to an apparatus and method for learning and storing an engine friction torque upon engine startup when an engine is driven through a Hybrid Starter & Generator (HSG), and an Engine Push with Fuel Cut Off (PUC) diagnosis is performed in a hybrid vehicle.
(b) Background Art
Hybrid vehicles are next generation vehicles which improve the fuel efficiency of a vehicle and significantly reduces the emission of harmful gases. Hybrid vehicles include both an internal combustion engine and an electric motor and perform driving of the internal combustion engine or of the electric motor in accordance with the operating conditions of a vehicle.
Furthermore, plug-in hybrid vehicles have been mass-produced recently. The plug-in hybrid vehicle plugs into an electrical outlet to charge its battery and runs by driving a motor with the charged battery. Since the plug-in hybrid vehicle is driven by an oil engine when the charge amount of the battery drops to a certain level or less, the plug-in hybrid vehicle has higher fuel efficiency than general hybrid vehicles.
The hybrid vehicle and the plug-in hybrid vehicle include an engine and a plurality of motors and may further include a Hybrid Starter & Generator (HSG) directly connected to the engine. Accordingly, the hybrid vehicle and the plug-in hybrid vehicle can drive the engine through the HSG without a combustion process of an internal combustion engine.
Thus, since the HSG equipped in the hybrid vehicle or the plug-in hybrid vehicle is configured to be connected to an engine pulley, the engine may be forcibly revolved through the driving of the HSG. Furthermore, the HSG connected to the battery serves to convert a torque generated in the engine into battery charging energy.
Since the hybrid vehicle and the plug-in hybrid vehicle include an engine system as a component generating a driving force, it is necessary to determine a drag torque of a drive engine or loss torques of auxiliary units, which are determined by the internal friction of the drive engine in order to operate the engine system. Typically, this is performed using characteristics curves or characteristic maps which determine the drag torque or the loss torque, e.g., in accordance with the operating point or in accordance with state variables of the drive engine. In order to compensate for deviations of loss torques provided in the characteristics curves or the characteristic maps, shown by part tolerances due to the manufacturing reasons or for the durability life of the engine system, generally, these deviations are permanently, continuously, or regularly applied.
The internal combustion engine for applying the loss torque requires very limited operating conditions. In case of existing gasoline vehicles, the idle state of the engine is required to compensate for the torque deviation of the engines However, since the idle state is minimized to improve the fuel efficiency in the hybrid vehicle and the plug-in hybrid vehicle, there is a difficulty in performing typical engine friction torque learning.
FIG. 1 is a view illustrating engine torque Proportional Integral Derivative (PID) control for setting a target engine RPM when there is no external change in an idle state of an engine according to a related art. As shown in FIG. 1, when the target engine RPM is maintained, the integral control for a torque generated in the engine is performed.
In another related art, Korean Patent Application Publication No. 10-2013-0088206 (hereinafter, referred to as Reference 1) discloses an apparatus and method of learning engine torque, which stores engine torque execution completion data and learning values about engine torques obtained by learning engine torques in idle mode when there exist engine torque learning execution completion data and engine torque learning values in idle state. However, in Reference 1, the apparatus performs PID control through idling of an engine, and there is a limitation in learning an engine friction torque in a hybrid vehicle and a plug-in hybrid vehicle which minimize the engine idle state. Furthermore, since learning is performed through the driving of the engine during the stop of a vehicle, there is a limitation in that it is difficult to perform accurate engine friction torque learning.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the disclosure, and therefore, it may contain information that does not form the related art that is already known in this country to a person of ordinary skill in the art.